Thing is, the Conservatives have already promised not to increase taxes.

The gesture is a symbolic one, enshrining in law what Harper has already repeatedly promised and allowing him to say other parties — should they form future governments — would have to break the law in order to raise taxes.

The Liberals have promised to increase taxes on the wealthiest one per cent, while the NDP want to raise the corporate tax rate.

Another government could also just repeal the legislation.

So if Canada finds itself with a minority Conservative government after Oct. 19, would Harper let the other parties topple his new government over it, perhaps plunging the country into another election? Harper wouldn't say.

"I'm not going to get into discussing hypothetical situations," he said with a smile.

The "tax lock" is a direct lift from British Prime Minister David Cameron's re-election playbook.

It also bears the fingerprints of right-wing campaign consultant Lynton Crosby, an Australian who is working with the Conservatives. Crosby is credited with having helped secure election victories for Cameron and Australian Prime Minister John Howard.

Harper's legislation would prohibit increases to federal personal and business income taxes, sales taxes and "discretionary payroll taxes" such as employment insurance and the Canada Pension Plan.

The Conservatives say the law would still allow them to close tax loopholes and address "tax avoidance schemes."

Asked if there would be any consequences to a government breaking the "tax lock," Harper didn't name any — beyond the political.

"There are particular consequences for Conservative governments because people expect Conservative governments in particular to keep taxes down, but when you make a commitment there is a cost to breaking that commitment that's very high," he said.

"I could cite a former president of the United States around that, but I won't get into that particular discussion."

That appeared to be a reference to George Bush, the one-term U.S. president whose famous 1988 promise — "Read my lips: No new taxes" — was broken in 1990 and came back to haunt him in 1992, when he lost to Bill Clinton.

Not surprisingly, Harper made political hay Friday with the Finance Department's monthly fiscal monitor, which showed that Ottawa's surplus after four months of the 2015-16 financial year was about $5.2 billion.

"We have yet another contrast between our Conservative economic action plan and the reckless spending promises of the Liberals and NDP," Harper said.

"We are well on track for the second balanced budget in a row at the federal level."

Earlier this month, the Finance Department said the government finished the 2014-15 fiscal year with a $1.9-billion surplus, the opposite of the $2-billion shortfall that was predicted in the spring budget.

The 2014-15 surplus ended a streak of six straight deficits under the Conservatives.

Harper has been relentlessly promoting his economic stewardship throughout the campaign, but Friday he also took a Quebec-specific message to a closely watched riding.

In 2011, the Conservatives lost

Montmagny-L'Islet-Kamouraska-Riviere-du-Loup to the NDP by nine

votes as the orange wave swept the province.

Harper, who used Thursday's French leaders' debate to turn the niqab controversy to his advantage, kept the issue front and centre on Friday.

His position that new Canadians should not wear face coverings while swearing their citizenship oath plays well in Quebec, where a taxpayer-funded poll suggests there is 93 per cent support for that idea.

On Friday, he essentially recited a new French-only Conservative ad in which he lumps the niqab issue in with low taxes, good jobs and a comfortable retirement as Quebec values the Tories protect.